This invention relates to an ink delivery system for acoustic ink printing applications utilizing an acoustic ink printhead having droplet emitters aligned with orifices. More particularly, the invention is directed to a relatively compact, sealless system that provides high speed, pulseless and uniform flows of ink through multiple acoustic ink printheads. The system enables the correct positioning of the meniscus at every orifice of each of the different printheads by passively maintaining the ink pressure in each of the printheads independent of the ambient pressure, the volume of ink in each of the reservoirs or the amount of filter blockages. A single motor and a multi-head pump are also provided to the system. Further, the system comprises a heating means, a cooling means and thermal sensing means for each printhead to enable maintenance of the ink temperature in each of the printheads independent of the image (consequently ejection energy) content. In addition, the system includes an ink reservoir utilizing an ink filter and an ink level sensing arrangement. In an alternative embodiment, the ink is delivered through the printhead by using a segmented manifold on the printhead so that multiple ink colors can be printed by a single printhead.
While this invention is particularly directed to the art of acoustic ink printing, and will thus be described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may have application with any type of printhead where a uniform, constant, high speed flow of ink is utilized, to cool/maintain the temperature of the printhead while the ink pressure is maintained/kept uniform for uniform printing. The invention may also find application in fields where materials other than ink are emitted from an acoustic emitter.
By way of background, it has been shown that acoustic ink printers which have printheads comprising acoustically illuminated spherical or Fresnel focusing lenses serving as droplet emitters can print precisely positioned picture elements (pixels) at resolutions that are sufficient for high quality printing of complex images. Significant effort has gone into developing acoustic ink printing, see for example, U.S. Pat. Nos. 4,308,547; 4,697,195; 4,751,530; 4,751,534; 5,028,937; and 5,041,849, all of which are among many commonly assigned to the present assignee.
Although acoustic lens-type droplet emitters currently are favored, there are other types of droplet emitters which may be utilized for acoustic ink printing, including (1) piezoelectric shell transducers, such as described in Lovelady et al., U.S. Pat. No. 4,308,547, and (2) interdigitated transducers (IDTs), such as described in commonly assigned U.S. Pat. No. 4,697,195. Furthermore, acoustic ink printing technology is compatible with various printhead configurations including (1) single emitter embodiments for raster scan printing, (2) matrix configured arrays for matrix printing, and (3) several different types of page and width arrays, ranging from (i) single row sparse arrays for hybrid forms of parallel/serial printing, (ii) multiple row staggered arrays with individual emitters for each of the pixel positions or addresses within a page width address field (i.e., single emitter/pixel/line) for ordinary line printing.
For performing acoustic ink printing with any of the aforementioned droplet emitters, each of the emitters launches a converging acoustic beam into a pool of ink, with the angular convergence of the beam being selected so that it comes to focus at or near the free surface (i.e., the liquid/air interface), or meniscus, of the pool. Moreover, controls are provided for modulating the radiation pressure which each beam exerts against the free surface of the ink. That permits the radiation pressure from each beam to make brief, controlled excursions to a sufficiently high pressure level to overcome the restraining force of surface tension, whereby individual droplets of ink are emitted from the free surface of the ink on command, with sufficient velocity to deposit them on a nearby recording medium.
Maintenance of pressure in the acoustic ink printhead relative to the meniscus is an important factor in maintaining uniform print quality. The position of the meniscus in the opening, or orifice, provided for emission of ink is required to be held constant so that the focussed beam consistently converges at or near the surface of the pool. Further, the temperature of the ink in the printhead should be prevented from increasing or decreasing in order to maintain the physical properties of the ink important for correct ejecting.
A main attraction of acoustic ink printing is the ability to control droplet size based on the frequency of the signal provided, rather than relying on the size of the nozzle emitting the droplet. For example, an AIP printer may emit droplets that are a magnitude in size smaller than the AIP openings. On the other hand, conventional ink jet printing requires a minimization of the nozzle itself to obtain small droplets.
It is desirable in an acoustic ink printing system to have a suitable ink delivery system. Specifically, the ink delivery system should deliver ink to the printheads of the printer at uniform, pulseless high flow rates. The reason for these requirements is that, as alluded to above, the process of printing using an acoustic ink printing system is very precise. Therefore, the flow rate to the printheads must be uniform and pulseless to avoid degradation in the process.
In addition, it is desirable in an acoustic ink printing system to maintain the pressure and temperature in the printhead at a uniform level because maintaining the meniscus of the ink in the openings noted above is very important to acceptable operation of the system. Known approaches to maintaining the pressure include controlling the voltage of the motor that drives the pump heads that pump the ink and providing feedback from pressure sensors attached to the ink line. However, these approaches require the use of regulators and sensors to maintain pressure. It would be desirable to avoid the use of such extraneous components in spite of changing environments and varying amounts of ink in the circuit, as well as small increases in resistance in the ink filter and the heat exchanger over the life of the printer.
Further, it is desirable, for certain applications, to address difficulties noted above and deliver multiple colors of ink to a single printhead.
Thus, the present invention contemplates a new ink delivery system that finds particular application-with acoustic ink printheads and overcomes the heretofore known difficulties.
An ink delivery system for use with an acoustic ink printer having incorporated therein at least one acoustic ink printhead from which ink is emitted is provided. The invention is directed to a relatively compact, sealless system that provides high speed, pulseless and uniform flows of ink maintained at constant temperature and pressure through the acoustic ink printheads, which is robust over external conditions.
In one aspect of the invention, the system comprises a motor having a drive gear/pulley, an ink reservoir having a bottom portion with a first passageway defined therein, the reservoir also having a heater and a filter disposed therein, a pump head having disposed therein first and second pump gears positioned for operative engagement with one another to drive ink received from the ink reservoir through the first passageway out of the pump head through an outlet, a drive shaft extending from the first pump gear through a second passageway of the ink reservoir and through the ink reservoir to a shaft gear/pulley operatively engaged to the drive gear, a heat exchanger optionally positioned to receive ink driven out of the pump head through the outlet, an inlet line from the heat exchanger to the printhead inlet and a return line from the printhead outlet back to the ink reservoir, the return line having an exit end open to the ambient, and a funnel-like structure attached to a manifold plate positioned on top of the ink reservoir that receives the returning ink and returns it to the ink reservoir through internal passages in the manifold plate.
In another aspect of the invention, the position of the exit end of the return line is adjustable relative to the ink orifice plane of the printhead.
In another aspect of the invention, the exit end of the return line is exposed to ambient pressure.
In another aspect of the invention, the heater and heat-exchanger is selectively operated.
In another aspect of the invention, the filter is a pleated filter that defines a substantially exterior region of the reservoir into which the return ink is delivered, thereby the return ink travels through the pleated filters into a sealed inner region of filtered ink which is connected to the inlet port of the pump.
In another aspect of the invention, a segmented manifold is provided to each printhead of the system to allow for delivery of multiple colors of ink to a single printhead.
Further scope of the applicability of the present invention will become apparent from the detailed description provided below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.